This invention relates to polymerizable compositions.
Known methods of producing molded products by in-mold curing of polymerizable composition include the resin transfer molding (RTM) whereby a polymerizable composition is transferred into a mold for curing, the casting molding, the reaction injection molding (RIM) and the pultrusion whereby a bundle of fibers for reinforcement is preliminarily impregnated with a polymerizable composition prior to an in-mold curing process. The present invention relates to a polymerizable composition containing unsaturated urethane of a specified structure, alkyl (meth)acrylate and thermoplastic macromolecular compound capable of dissolving in or swelling by impregnating alkyl (meth)acrylate. The invention also relates to a method of producing molded products with improved dimensional stability and surface property by in-mold curing of such a polymerizable composition at a specified initial mold temperature.
As examples of polymerizable compositions containing unsaturated urethane having within its molecule a group with radical polymerization characteristics and a urethane bond, U.S. Pat. No. 4,480,079 has proposed those containing polyisocyanates having more than two isocyanate groups in the molecule or polyurethane polyisocyanates, unsaturated urethane obtainable from hydroxyalkyl (meth)acrylate, and alkyl (meth)acrylate. If a product is produced by in-mold curing of such a prior art polymerizable composition containing unsaturated urethane obtained from polyisocyanates and hydroxyalkyl (meth)acrylate, however, the mold shrinkage is large due to the structure of the unsaturated urethane and, as a result, one can obtain only molded products with poor dimensional stability and surface property with prominent visual discernment of reinforcing fiber patterns. Even if use is made of a low shrinking agent containing known thermoplastic macromolecules in order to reduce the mold shrinkage, there is a phase separation of the low shrinking agent on the surface of the molded product. In other words, there is hardly any preventive effect on the mold shrinkage and the molded product has its surfaces contaminated by the phase-separated low shrinking agent. If a product is obtained by in-mold curing of the aforementioned prior art polymerizable composition containing unsaturated urethane obtainable from polyurethane polyisocyanate and hydroxyalkyl (meth)acrylate, its mold shrinkage is smaller than if unsaturated urethane is used and there are some improvements in dimensional stability and surface property but the degree of such improvements is not satisfactorily large. Even if a low shrinking agent is used together, the mold shrinkage cannot be further improved.
U.S. Pat. No. 4,374,229 has proposed polymerizable compositions containing unsaturated urethane and vinyl monomers obtainable by coupling oligomer polyester having hydroxy end group at one end and vinyl end group at the other end with polyisocyanate. Even if such polymerizable compositions are used for in-mold curing, one can obtain only products with poor dimensional stability and surface property as in the case of using the prior art polymerizable composition, and the additional use of a low shrinking agent hardly has any effect.